The overall goal of this study is to determine if treatment with aminohydroxybutylidine diphosphonate (ABD) would avert the development of hypercalciuria, hyperphosphaturia, negative calcium balance and increased propensity for the crystallization of stone-forming calcium salts in normal subjects undergoing prolonged bedrest. This project will test the hypothesis that ABD could prevent osteoporosis and nephrolithiasis during space flight by inhibiting bone resorption, utilizing the model of bedrest immobilization.